ed of goat has specific weight ranges, which vary from more than 140 kg (310 lb) for bucks of larger breeds such as the Boer, to 20 to 27 kg (44 to 60 lb) for smaller does. Within each breed, different strains or bloodlines may have different recognized sizes. At the bottom of the size range are miniature breeds such as the African Pygmy, which stand 41 to 58 cm (16 to 23 in) at the shoulder as adults. Most goats naturally have two horns, their shape and size depending on the breed. There have been incidents of polycerate goats (having as many as eight horns), although this is a genetic rarity. Unlike cattle, goats have not been successfully bred to be reliably polled, as the genes determining sex and those determining horns are closely linked. Breeding together two genetically polled goats results in a high number of intersex individuals among the offspring, which are typically sterile. Their horns are made of living bone surrounded by keratin and other proteins, and are used for defense, dominance, territoriality, and thermoregulation. Both male and female goats may have beards, and many types of goat (most commonly dairy goats, dairy-cross Boers, and pygmy goats) may have wattles, one dangling from each side of the neck. Goats have horizontal, slit-shaped pupils, allowing them to see well by both night and day, and giving them a wide field of vision on either side to detect predators, while avoiding being dazzled by sunlight from above. Goats have no tear ducts. Goats are ruminants. They have a four-chambered stomach consisting of the rumen, the reticulum, the omasum, and the abomasum. As with other mammal ruminants, they are even-toed ungulates. The females have an udder consisting of two teats, in contrast to cattle, which have four teats. An exception to this is the Boer goat, which sometimes may have up to ei